In three dimensional-high efficiency video coding (3D-HEVC), which is latest recent international standard for 3D video coding, an intra-frame skip mode is used as a coding technology for depth image coding. Intra-prediction includes predicting a pixel in a current coding block by using reconstruction values of other pixels that are spatially adjacent to the current coding block. The adjacent pixels used for prediction and the pixel in the current block that is to be predicted are in the same image frame, and thus this method is called intra-prediction. In a conventional intra-coding mode, a difference between a predicted pixel value after intra-prediction and an original pixel value may be calculated, and then encoded into a video bitstream that is transmitted to a decoder. Also, the decoder may add the difference to the predicted pixel value obtained by performing the same intra-prediction, so as to obtain a reconstructed pixel value. An intra-skip mode of 3D-HEVC also performs intra-prediction. However, in the intra-skip mode, after the intra-prediction, a reconstructed pixel value may be directly set to a predicted pixel value and other information in a bitstream may not be transmitted. Also, compared to an original value before coding, the reconstructed value may have a certain distortion due to the lack of compensation using a difference. However, since the difference is not transmitted in the bitstream, coding compression efficiency may be improved. A depth image includes a plurality of flat blocks. Since a difference between an original value of a pixel in a flat block and a predicted value obtained by using pixels adjacent to the pixel is so small that distortion of a reconstructed value is also very small even when the difference is not transmitted. Therefore, an intra-skip mode is used for depth image coding in 3D-HEVC.
Intra-prediction may provide many prediction methods such as a vertical method, a horizontal method, and a right-down diagonal method. When it is determined to encode a current block by using an intra-skip mode, an encoder still needs to select an intra-prediction method to be used. Next, the encoder may transmit information of the intra-prediction method in a bitstream so that a decoder knows the intra-prediction method to be used when decoding the current block.
In 3D-HEVC, a flag may be fixedly transmitted in a bitstream to indicate whether a current block is coded in an intra-skip mode. When the block is coded in the intra-skip mode, an index is transmitted subsequently to indicate an intra-prediction method. The index is fixedly associated with the intra-prediction method. Specifically, an encoder and a decoder may determine a common order of all supported intra-prediction methods, and the encoder may transmit an index of an intra-prediction method used in the decoder. The order of the intra-prediction methods is not changed, i.e., the same intra-prediction method is always associated with the same index value.